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VEGETATION - 2000

Lake Maggiore - Italy, 3-6 April 2000


Fire Scar Detection in the Canadian Boreal Forest

Plummer, S.E., Gerard, F.F. and Wyatt, B.K.
Centre for Ecology and Hydrology, Monks Wood, Abbots Ripton,
Cambs, PE17 2LS, UK
Tel: +44 1487 772475, Fax: +44 1487 773467, Email: sp@wpo.nerc.ac.uk

Paper (pdf file, 310 k)

The boreal ecosystem stretches across the Northern Hemisphere’s circumpolar countries. It covers approximately 10% of the Earth’s land surface, ranking second in terms of total plant mass to the tropical forest belt. Because it contains approximately 40% of terrestrial carbon, it plays an extremely important role in the global carbon budget. It is therefore important to identify anything that perturbs this ecosystem, for example, fire. However, global terrestrial carbon cycle models generally do not take into account loss of carbon through disturbance. Further, disturbance has a strong influence on succession in the boreal ecosystem through the effect on opportunities for change from boreal biotopes to others typical of biomes to the south and north. Since climate change may alter the frequency and size of disturbance events, it is vital to monitor changes in their spatial and temporal occurrence if we are to predict the impacts of global environmental change. Yet, currently there is no comprehensive database of disturbance across the entire boreal ecosystem and, where efforts to collate information have been attempted, they have usually been either spatially restricted or a snapshot in time. Air photo interpretation and visual annotation of base maps from light aircraft are the primary methods for fire mapping. This is an extremely labour intensive method of fire scar mapping which requires considerable financial investment. For the boreal forest, the large area of individual burns makes coarse resolution remote sensing an attractive alternative although it is limited to the last 25 years.

This paper extends the work of Eastwood at al. (1998) on fire scar detection through the comparison of new indices, thresholding and segmentation of VEGETATION data over the BOREAS experimental region. Imagery on a monthly time-step was acquired through the 1998 active fire season (May-September). Segmentation was performed on a total of 24 VEGETATION images to assess sensitivity of the approach to segmentation criteria and the variability of fire scar detection as a function of image geometry and atmospheric state. The results were compared against hot spot observations recorded for the time period in the FIRE-M3 detection system (http://fms.nofc.cfs.nrcan.gc.ca/FireM3/) (Li et al. 1997). Older fire scars were identified with reference to the Canadian Forestry Service GIS database of large fires covering the period 1980-92 as used by Eastwood et al. (1998). The results are in accordance with the observations by Eastwood at al. (1998) that the middle infrared waveband provides better spectral differentiation of fire scars than methods based on NDVI.